1. Field of the Invention
The present invention relates to a liquid crystal display device (LCD) and, more particularly, to an LCD having an alignment mark in a pixel region.
2. Description of the Related Art
In general, the LCD includes two substrates separated with a certain gap therebetween, liquid crystal inserted between the two substrates, and a plurality of layers formed between the two substrates and liquid crystal.
Alignment marks are formed on the two facing substrates and used as reference points for aligning the two substrates for their attachment. That is, an operator of an alignment process can determine a degree of alignment of the two substrates by recognizing whether the alignment mark patterns on the two substrates are identical or not.
The alignment marks are formed on a non-active region of the substrate on which elements are not formed, and when the aligning process is finished, the non-active region with the alignment marks are cut away to be discarded.
Recently, in order to implement full colors similar to natural colors, there has been a tendency to provide greater integration of the LCD elements to make the element smaller and to increase their density, resulting in gaps between elements being quite narrow.
Thus, even if the alignment is deviated slightly, the corresponding elements may be formed away from their originally intended positions, degrading color reproducibility and yield. Therefore, the aligning is of importance.
The alignment marks of the related art LCD will be described with reference to the accompanying drawings.
FIG. 1 is a plan view showing alignment marks formed on the substrate of the related art LCD. As shown, a substrate 1 can be divided into an active region 3 on which various elements are formed, and a non-active region 5 that can be cut away to be discarded when the processes are completed. Alignment marks 7 in a typical cross shape are formed on four corner portions of the non-active region 5.
The alignment marks are generally formed on the substrate in the early processes of upper and lower substrates, and used when the upper and lower substrates are attached.
When the upper and lower substrates of the LCD are attached with liquid crystal therebetween, the alignment marks of the upper substrate and alignment marks of the lower substrate appear to overlap with each other, so an operator can determine that the upper and lower substrates are properly attached.
In general, the alignment marks are formed on the corner portions of the upper and lower substrates. If two alignment marks are used, they are typically formed on one corner portion and the other diagonally corresponding comer portion. Alternatively, if four alignment marks are used, they can be formed on each corner portion as necessary. In some cases, only one alignment mark can be used and formed on one corner portion.
The alignment marks is too minute to be recognized by the eyes of the operator, so the alignment mark is recognized by using a microscope to determine a degree of alignment of the substrates.
However, the alignment marks of the LCD according to the related art allow merely the overall alignment of substrates, failing to check a precise degree of attachment between lines or elements in an active region, namely, a degree of misalignment.
Actually, during the fabrication process, the LCD undergoes a high temperature process such as a plurality of exposure processes and a testing, and in the processes, the glass substrate may be distorted, leading to distortion of line patterns. Then, the precise degree of alignment between lines or elements can hardly be recognized through only the alignment marks formed on the corner portions of the substrates.
In addition, the internal distortion phenomenon becomes severe as the substrates are increased in size and the lines become more minute and fine.